BUFFALO, N.Y. - The NHL has suspended Buffalo Sabres forward Zenon Konopka for 20 games after he tested positive for a banned substance.

In announcing its decision Thursday, the NHL did not reveal what substance was discovered in the player's system.

In a statement released through the NHL Players' Association, Konopka accepted responsibility for the positive test. Konopka wouldn't specify what the substance was except to say it was an ingredient found in an over-the-counter product.

Konopka's future was already uncertain in Buffalo because he is eligible to become an unrestricted free agent in July. The NHL said the 20-game ban will be enforced once the player signs a new contract.

The Sabres claimed the 33-year-old journeyman off waivers in January after he was released by Minnesota.